[analyzer] Document the issue hash debugging facility

Differential Revision: https://reviews.llvm.org/D39543

llvm-svn: 318030
diff --git a/clang/docs/analyzer/DebugChecks.rst b/clang/docs/analyzer/DebugChecks.rst
index e2a8e05..67521b8 100644
--- a/clang/docs/analyzer/DebugChecks.rst
+++ b/clang/docs/analyzer/DebugChecks.rst
@@ -242,6 +242,19 @@
       clang_analyzer_printState(); // Read the stderr!
     }
 
+- ``void clang_analyzer_hashDump(int);``
+
+  The analyzer can generate a hash to identify reports. To debug what information
+  is used to calculate this hash it is possible to dump the hashed string as a
+  warning of an arbitrary expression using the function above.
+
+  Example usage::
+
+    void foo() {
+      int x = 1;
+      clang_analyzer_hashDump(x); // expected-warning{{hashed string for x}}
+    }
+
 Statistics
 ==========